The present invention relates to a serial communication device used for coupling an upper controller to motor drivers to be controlled by this upper controller, and it also relates to the motor drivers.
An upper controller is coupled to a plurality of motor drivers via serial communication, and an operation command is supplied to the motors through this serial communication. This structure has prevailed recently in the market because of saving cables and more sophistication. For instance, an upper controller is an NC controller, and motor drivers are servo drivers that drive servo-motors. In this case, an operation command such as a position command, a speed command or a torque command is often supplied to the motor drivers from the upper controller.
A serial communication is shown in FIG. 12, and 100BASE-T Standard is applied to the physical layer of the serial communication, thereby forming the foregoing instance. In FIG. 12, upper controller 1 incorporates first communication IC 3 and first communication connector 2. Both the elements work for transmitting and receiving a serial communication, and are equipped with receiving terminals 3r, 2r and transmitting terminals 3t, 2t. They are connected to each other respectively. In an actual operation, a pulse transformer is disposed between IC 3 and connector 2; however, they are omitted here to avoid complexity. Also in the actual operation, a pair signal formed of two transmission signals or two receiving signals is used; however, the respective signals are simplified to a single signal in the drawings.
Motor driver 4 incorporates first IC 3 and first communication connector 2 similarly to upper controller 1, and signals are transmitted or received also in a similar way to upper controller 1. A plurality of motor drivers 4 are prepared in general, and three motor drivers are disposed as an example in the case of FIG. 12. Hub 5 works as a relay of communication data and is equipped with many of the same connectors as first connector 2.
As a whole, upper controller 1 and all the motor drivers 4 are coupled with respect to hub 5 via first communication cables 6, each of which has a transmitting path and a receiving path independent of each other. The 100BASE-T STD specifies that first cable 6 uses four pairs of twist-pair lines (8 lines), and first connector 2 uses RJ-45 modular jack.
The foregoing structure employs, in general, a master-slave method for communication, i.e., a master station issues a command and a slave station responds thereto. In FIG. 12, upper controller 1 is assigned to a master and motor drivers 4 are assigned to slaves. A command data issued by upper controller 1 is transmitted to one of motor drivers 4 via hub 5, and a response data from the motor driver 4 is transmitted to upper controller 1 via hub 5. After completing a transmitting/receiving data to/from one of motor drivers 4, upper controller 1 then starts transmitting/receiving data to/from another motor driver 4. This operation is repeated sequentially through every motor driver 4 before one communication cycle is completed. This communication cycle is executed repeatedly, thereby realizing a real-time transmission.
The conventional structure discussed above forms so called xe2x80x9ca star wiringxe2x80x9d having hub 5 at the center in a transmission path. However, a radial configuration of upper controller 1 and motor drivers 4 with hub 5 at its center is practically not used because it takes space. The configuration as shown in FIG. 12, namely, upper controller 1 and motor drivers 4 are arranged side by side, is regularly used. In this case, first cables 6 are forced to be bundled at some place, which lowers wire-routing efficiency. An objective of the serial communication, i.e., save-wiring, is thus not sufficiently satisfied. Further the presence of hub 5 increases the cost of the entire system.
The present invention provides a serial communication device to be used for controlling a motor, the serial communication device comprising the following elements:
(a) an upper controller including:
(a-1) a first communication IC for controlling a communication of a set of transmitting and receiving;
(a-2) a first communication connector having a transmitting terminal connected to a transmitting terminal of the first IC and a receiving terminal connected to a receiving terminal of the first IC; and
(b) motor drivers, each one of them including:
(b-1) a second communication IC for controlling a communication of a set of transmitting and receiving;
(b-2) a second communication connector having a receiving terminal connected to a receiving terminal of the second IC;
(b-3) a third communication connector having a transmitting terminal connected to a transmitting terminal of the second IC, and a receiving terminal connected to a transmitting terminal of the second connector.
In the foregoing structure, a first communication cable having independent paths for transmitting and receiving is used to connect the upper controller to the motor driver disposed in the front-most stage. In connecting the motor drivers to each other, the first cable connects the third connector of a first motor driver to the second connector of a second motor driver. In the motor driver disposed in the back-most stage, a coupling element that connects a transmitting terminal to a receiving terminal is connected to a third connector. The upper controller is daisy-chained to the respective motor drivers.